Observing Silver Nanoparticles in Real Time

Figure 1. Researchers at Ruhr-University Bochum are using dark-field microscopy to observe silver in real time as individual nanoparticles, with each nanoparticle experiencing chemical reactions.

Silver nanoparticle systems are commonly used in medical treatments, food, and sports products for their antibacterial and anti-inflammatory properties; however, more research is needed to understand how such nanoparticles react in biological systems. Doctor Kristina Tschulik and researchers from Ruhr-University Bochum in Germany used a novel combination of electrochemical and spectroscopic methods to observe silver nanoparticle behavior in real time. With these methods, the researchers observed how silver nanoparticles could transform into poorly soluble silver chloride particles under specific conditions.

To perform this analysis, the researchers mimicked the silver oxidation conditions present within biological environments. A potential was applied to measure the current experienced by the silver nanoparticles. The researchers used dark-field microscopy — microscopy that excludes unscattered beams from desired images — along with a spectrophotometer and an electrochemical cell to analyze oxidation-reduction reactions among silver nanoparticles immersed in chloride solution. Cyclic voltammetry — a technique that measures current in an electrochemical cell under conditions of excess voltage — was used to measure the intensity and real-time position of nanoparticle resonance.

The mass spectroscopy results revealed that silver peak positions had decreased optical signal intensities; the researchers suggested that this change was due to the reversible formation of silver chloride amidst the available oxidation-reduction reactions. The spectroscopy results for more positive reduction potentials revealed more transformations from silver to separate compounds such as silver oxide or chlorite. Electrochemical currents were not directly observed, allowing the researchers to suggest that electrochemistry, when combined with dark-field microscopy, could be used to analyze nanoparticle reactions with individual subjects and real-time conditions. These results also showed that the electrochemical cells’ current signals could correlate to the chemical conversion steps associated with specific nanoparticles. The researchers have suggested that these techniques may be used for improvements in studies concerning nanomaterials, electrochemical degradation under various conditions, and the cellular uptake of chemical compounds.